The invention discloses a yarn feeding device of a hosiery knitter. The prior rubber string knitting device conducts yarn feeding from the outer side of a knitting needle cylinder, so that cut rubberstring heads are exposed on the outer surface of a rib top of a sock. The yarn feeding device of the hosiery knitter comprises a yarn feeding rack, a sock body yarn feeding rack and a rubber string yarn feeding mechanism. Sock knitting holes are formed in the yarn feeding rack. The sock body yarn feeding rack is fixed on the yarn feeding rack. The rubber string yarn feeding mechanism comprises a rubber string spring, a first fixing block, a rotary block, a turnover handle, a hinge shaft, a limiting bolt, a rubber string air cylinder and an L-shaped shuttle head. The L-shaped shuttle head is composed of a fixing rod and a yarn feeding rod which are integrally molded. The feeding device of the hosiery knitter yarn can make the rubber string enter into the knitting needle cylinder to performknitting from the inner side of the knitting needle cylinder, so that string heads generated by cutting the rubber string are reserved in the sock, and the quality and the appearance degree of the knitted sock are improved.